During production of the oil-gas well, no matter whether the well is a vertical well or a horizontal well, due to factors such as heterogeneity of oil reservoir, the well needs to be packed off into a plurality of relatively independent zones for production, and flow is controlled in segments for production. The oil-gas well production here comprises output and injection of a fluid during production of the oil-gas well, such as petroleum exploitation, or injection of water, gas, a chemical agent for improving a recovery rate of the oil field or the like, into the formation during production, or injection of an acid liquid into the formation during some operations.
The oil-gas well is packed off into a plurality of relatively independent zones for production usually by a method of using a flow-control device in combination with a device of separating the production segment of the oil-gas well into several flow units in an axial direction of the oil-gas well, for example, by a method of using a flow-control filter string plus a packer.
For the sake of prevention of sand, a sand control screen is provided for many wells in the oil-gas field. FIG. 1 shows a structure of an oil-gas well into which a sand control screen is already run, comprising a well wall 1, a sand control screen 2, a clearance 3 between the sand control screen and the well wall, and a packer 4 for hanging the sand control screen. Those skilled in the art can all appreciate that the clearance 3 between the sand control screen and the well wall comprises but is not limited to an entire annular clearance between the sand control screen and the well wall or a partial annular clearance which is partially collapsed between the sand control screen and the well wall or other similar interval space.
In many oil-gas wells, production of segmental flow control is implemented by running the flow-control filter string and the packer in the well, and actively packing off the clearance between the flow-control filter string and the well wall by adding the packer to the flow-control filter string, i.e., obstructing an axial channeling flow passage outside the flow-control filter string to achieve better production of segmental flow control.
However, the manner of the flow-control filter string plus the packer has serious problems in the oil-gas well into which the sand control screen is already run. As shown in FIG. 2, in the oil-gas well into which the sand control screen is already run, there is an unpacked-off clearance between the sand control screen and the well wall. Since this kind of clearance can form an axial channeling flow passage, it damages the pack-off effect between the flow-control filter string in the sand control screen and the sand control screen, and therefore leads to failure to achieve very good production of segmental flow control. FIG. 2 further discloses a flow-control filter string 5, a flow-control filter 6 on the flow-control filter string, a packer 10 disposed in an annular space between the flow-control filter string and the sand control screen, and a hold-down packer 8 for hanging the flow-control filter string. The arrow in the figure indicates the flow direction of a channeling fluid such as water. As shown in FIG. 2, the channeling fluid such as water enters the clearance between the well wall and the sand control screen through the well wall, forms an axial channeling flow in the clearance between the well wall and the sand control screen, and then enters the flow-control filter string, thereby ruining the pack-off effect between the flow-control filter string in the sand control screen and the sand control screen, and failing to achieve an excellent production of segmental flow control.
As can be seen from the above, in order to achieve production of segmental flow control by using the flow-control filter string plus the packer in the oil-gas well into which the sand control screen is already run, there is a need to draw out the sand control screen already run into the oil-gas well, and then run the flow-control filter string and the packer. However, in many cases, since the sand control screen is very long, the resistance between the sand control screen and the well wall is very large, which resistance is caused largely because sand jam occurs partially on the sand control screen. Especially for a horizontal well, in a majority of situations, the sand control screen cannot be pulled out, and further, because its production segment is very long, the horizontal well particularly need to employ production of segmental flow control, so as to solve the problem of quick rise of water content in the produced liquid of the horizontal well, for example. Hence, this problem is relatively prominent, especially for horizontal wells.